Abstract
Equivalent widths and line widths of Ca II infrared triplet emission lines were measured in the high-resolution optical spectra of 39 young stellar objects. We found that the equivalent widths of the emission lines decrease with stellar evolution. It has often been claimed that strong chromospheric activity is generated by a dynamo process caused by fast rotation of the photosphere. However, we found no clear correlation between the strength of the Ca II lines and the stellar rotation velocity. Instead, we found that the objects with high mass accretion rates had stronger Ca II emission lines. This correlation supports the turbulent chromosphere model or the magnetic accretion theory for classical T Tauri stars. We also noticed that the equivalent widths of Ca II lines in transitional disk objects are one-tenth of those in classical T Tauri stars, even if the masses of the circumstellar disks are comparable.
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